The Boso Penisula area suffered from big slope failure disasters caused by Typhoon No. 25 carring torrential rainfall in September 1971.
Immediately after the disasters, we carried out the several investigations, that is, about the consciousness of residents for the slope failure, and the situations of slope failure using the ground investigation methods and the aerial photogrophic interpretation.
In this paper, we report the characteristics of slope failure which io one part of informations we got.
We classified the slope failure to 10 types taking note of geological and topographical conditions.
All of them, typical failure is the sliding of top soils on the Narita layer (sand layer) and the sliding or falling of top soils or weathering layer on the bedrock in the tertiary area.
The slope failures in the Narita layer area are apt to be dominated by something unusnal on the top of slopes and the location of mudstone layer lying between sand layer. The other hand, in tertiary area, the most inportant factors for slope failure are the locations of small valley on the slope and the dippression of surface plane on the mudstone layer.

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